Questions have been raised over how meat intended for dog food ended up in the human food chain in Northern Ireland as far back as 2005.

Despite the authorities finding out, there was no follow-up investigation, and the public was not told, a report by Professor Chris Elliott, director of the Global Institute for Food Security at Queen's University, found.

The Elliott Review suggested organised crime was behind the industrial-scale fraud, which could have raked in up to £3m.

The alarming news, published by the Department of the Environment, revealed: "It was strongly suspected that material found was part of an ongoing illegal business but for lack of the necessary investigative resource this was not pursued. The many leads that were opened into food crime networks at this time were not followed up."

Professor Elliott said the fraud occurred on an "industrial scale" across the UK.

The pet food meat involved in the scam is classified as fit for human consumption, but still contains material such as hide, hair, feathers and bones.

This 'category 3' meat looks no different to regular meat, making fraud harder to detect.

The 2005 meat consignment was found after a suspicious container arrived from Asia.

A follow-up operation was subsequently launched at a cold store which was not named in the report. Police, however, became involved after forged veterinary documents and a shrink-wrapping machine raised suspicions.

"It became evident that the primary business of the cold store was repacking and relabelling as fit for human consumption category 3 animal by-products meat," the report said.

An advertisement encouraged others in the industry to cut their losses by sending out-of-date stock to the illegal relabelling service.

"Evidence was found to demonstrate extensive criminal planning," but the report stated: "At that time there was no capacity for the major criminal investigation that the evidence and the criminal profits justified."

Professor Elliott said a new unit should be set up as a non-Home Office police force able to deal with "complex food crime perpetrated by highly organised and dangerous, potentially violent organised crime groups".

South Down MP Margaret Ritchie said the news was disturbing.

"It is deeply troubling to hear that dog food entered the food chain in an industrial scale in Northern Ireland, and that this was not adequately pursued when discovered in 2005," she said.

BACKGROUND

Meat is worth about £1 a kilo as pet food but if sold as mince for human consumption it would be worth £3.50 a kilo. There was a large quantity of beef fillets in the Northern Ireland scam, and Prof Elliott said if that was combined with mince the average price would have been at least £4 a kilo, making the criminal profit worth between £2.5m and £3m.